Download the .jar for NinjabrainBot as per usual from here.
Lets take an example where the .jar file is downloaded into the Downloads folder.
Now to add it as an application to your list of applications, create this file with the following contents under ~/.local/share/applications/NinjabrainBot.desktop
If the directory does not exist, then make the directory/directories by executing the following command in a terminal
mkdir -p ~/.local/share/applications/
Remember that the file name will change over versions. So as you update Ninjabrain Bot, you will have to change this file as well. Also, you will have to replace <user_name> with your username that you set during the install.
If you downloaded it elsewhere, then replace /home/<user_name>/Downloads/Ninjabrain-Bot-1.4.1.jar with the relevant path.
Now you can launch Ninjabrain Bot from your applications menu!